The invention relates to a connection between the rotor blade and rotor hub of a helicopter.
Helicopters having a rotor blade connection without joints and bearings normally contain a support beam (also called "flex beam") arranged between the lift-generating wing section and the rotor hub. The flex beam must securely transmit not only centrifugal and lateral forces, but also bending and torsional moments from the blade root to the rotor hub. Hence, it must simultaneously be constructed to be bending elastic about two axes, specifically usually flap-elastic in an area relatively nearer to the hub and lead-lag elastic in an area relatively nearer to the wing. Finally, it must also be as torsionally soft for permitting the blade angle adjusting movements about the longitudinal axis.
Vibrations in such a support beam are damped by means of an elastomer damper, which is either provided as a separate constructional unit between the rotor hub and the support beam or, as disclosed in German patent document DE 25 58 709 and German Patent Document DE 27 58 086, is applied in the manner of a surface-side coating directly to the support beam. However, in this case, it is difficult to connect a damper with a sufficiently large elastomer volume to the support beam structure in such a fashion that the individual elastomer layers are shear deformed as uniformly as possible under the effect of the rotational lead-lag movements of the rotor blades, as required in order to achieve an effective damping of the partially very small lead-lag bending-deformations of the support beam.
It is an object of the present invention to provide a rotor blade connection of the type mentioned above, in which the damping device is easily installed, and which achieves high-level structural damping with a large elastomer volume on a limited support beam length, without impairing the required stability and stiffness behavior of the support beam.
This object is achieved by the rotor blade connection, according to the invention, in which the damping device is arranged in slot-shaped notches of the support beam (which are required anyhow, to provide the necessary elasticity of torsion). This arrangement provides a space-saving housing of a large elastomer volume in the support beam structure itself. Because of such division into a plurality of slots and individual dampers extending in the direction of the main bending plane of the support beam, this arrangement ensures an extremely homogeneous or uniform shear deformation and a large-surface linking of the individual elastomer layers directly to the bending-deformed support beam sections. As a result both a high-level damping effect and a long useful life of the elastomer damper are achieved.
In another advantageous embodiment of the invention, intermediate layers of the individual dampers are each fixed to the support beam structure by singular fastening points, thereby preventing unintended relative displacements between the support beam structure and the intermediate layers, as well as disturbing shear distortions of the elastomer layers (for example, under centrifugal force). The damping effect of the individual elastomer dampers, however, is fully maintained.
Although the support beam slots and individual dampers may extend continuously along the whole bending-elastic support beam area, it is advantageous to divide the support beam slots in the longitudinal direction of the beam, and to arrange an individual damper in each partial slot in order to sensitively mutually coordinate the strength, stiffness and damping behavior of the support beam.
In another, particularly preferred, embodiment of the invention, the surface dimensions of the intermediate layers can be controlled electrically so that the shear deformation of the elastomer layers does not depend solely on the extent of the bending deformation of the support beam, but can also be influenced by external controls. As a result, the damping effect can be significantly improved mainly in the range of small bending vibrations of the support beam. To achieve a structurally simple control of the surface dimensions of the intermediate layers, these are preferably covered by electrically controlled piezo elements. Generally such piezo coatings can be used in connection with elastomer dampers only to a limited extent because of their high bending sensitivity; according to the invention, however, as a result of their special positioning, they are (like the intermediate layers) exposed to only very slight bending deformation and can therefore be used without any problems for controlling the damping effect. In order to provide an automatic control with desired control characteristics, the support beam is preferably equipped with a sensor arrangement for detecting bending vibrations of the support beam, and a control unit which activates the piezo elements according to the sensor signals.
As mentioned above, in the case of a helicopter rotor blade connection, mainly lead-lag bending vibrations of the support beam must be dampened. Correspondingly, the individual elastomer dampers are expediently arranged in the direction of the bending plane of the lead-lag elastic support beam section.
The support beam and/or the intermediate layers may be made of metal or preferably of a fiber reinforced material, in order to achieve favorable stiffness and stability behavior.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.